The mobile communication system has been developed for the user to communicate on the move. With the rapid advance of technologies, the mobile communication system has evolved to the level capable of providing high speed data communication service as well as voice telephony service. Recently, as one of the next generation mobile communication system, Long Term Evolution-Advanced (LTE-A) is on the standardization by the 3rd Generation Partnership Project (3GPP). LTE-A is a technology designed to provide a packet-based communication service at a data rate higher than those of the current communication technologies.
With the evolution of the 3GPP standard, many studies being conducted for optimization of radio networks as well as improvement of data rate. In the initial radio network configuration or optimization stage, a base station or a base station controller should collect radio environment information related to its own cell coverage, and this process is called Drive Test. The conventional drive test is very time-consuming and laborious task performed in such a way that an operator carries the test apparatuses on a vehicle while performing the measurement task repeatedly for a long time.
The measurement result is used to configure the system parameters of the base stations or base station controllers. Such a conventional drive test increases total costs and time of the radio network optimization and maintenance. Study on minimization of drive tests and enhancement of radio environment analysis process and manual configuration is being conducted in the name of MDT (Minimization of Drive Test). In more detail, the terminal measures the cell information and supplementary information on the neighbor eNBs. The terminal reports the radio channel measurement information to the eNB periodically or immediately in response to a specific event or after a predetermined time has elapsed from the time point when the radio channel measurement information has been logged. At this time, the UE operation of transmitting the measured cell information and other supplementary information to the UE is referred to as MDT measurement information report. If it is in the state capable of communicating with the eNB, the terminal transmits the neighbor cell information measurement result to the eNB immediately. Otherwise, if it is not in the state capable of communicating with the eNB, the terminal retains the logged measurement information and, when it becomes possible to communicate with the eNB, transmits the retained MDT measurement report.
In the following description, the radio channel information measured by the terminal and other supplementary information are referred to as MDT measurement information, and the operation transmitting the MDT measurement information from the terminal to a base station is referred to as MDT measurement information report. When reporting MDT measurement information, if it is possible to communicate with the base station, the terminal transmits the MDT measurement information immediately. Otherwise, it is impossible to communicate with the base station currently, the terminal waits until it becomes possible to communicate with the base station. The base station uses the MDT measurement information reported by the terminal for cell area optimization.
FIG. 1 is a diagram illustrating a concept of the MDT procedure according to the conventional technology.
The conventional drive test is performed in a way of measuring signal state while roaming around the service area to search for shadow areas on a vehicle carrying the measurement device. In MDT, the terminal performs this operation instead.
Referring to FIG. 1, a Network Monitoring System (NMS) 105 instructs to perform MDT. At this time, the NSM 105 provides an Element Manager (EM) 110 with configuration information necessary for MDT. The EM 110 generates MDT configuration to an evolved Node B (eNB) 115. The eNB 115 sends a User Equipment (UE) 120 the MDT configuration information to instruct to perform MDT as denoted by reference number 125. The UE 120 performs MDT to collect MDT measurement information. The MDT information may include location and time information as well as the signal measurement information. The collected MDT measurement information is reported to the eNB 115 as denoted by reference number 130, and the eNB 115 sends the MDT measurement information to a Trace Collection Entity (TCE) 135. The TCE 135 is a server for collecting MDT measurement information.
FIG. 2 is a signal flow diagram illustrating an MDT procedure for logging MDT measurement information in idle mode and reporting the MDT measurement information according to the conventional technology.
Referring to FIG. 2, the eNB 205 sends the UE 200 in idle mode the information necessary for configuring MDT, i.e. MDT configuration information. The MDT configuration information includes absolute reference time, sampling cycle, measurement duration, etc.
The sampling cycle is used for periodic downlink pilot signal measurement and the MDT measurement information is collected and logged at the predetermined period. The measurement duration denotes the total time for performing MDT. If the measurement duration passes, the UE stops MDT.
If the Radio Resource Control (RRC) state transitions from the connected mode to the idle mode, the UE starts MDT at step 215. After performing initial MDT measurement and log at step 220, the UE 200 continues MDT measurement and log at a sampling interval 230 indicated by the channel measurement configuration information at step 225.
At every MDT measurement and log period, the MDT measurement information is logged. For example, the MDT measurement information may include a Global Cell ID, Measurement Result, Location Information, Time Stamp, etc.
If the UE 200 enters the connected mode at step 235, it notifies the eNB 204 of the presence/absence of the logged MDT measurement information at step 240. The eNB 205 may request for the report depending on the situation. If there is a request from the eNB, the UE 200 reports the MDT measurement information logged until then and deletes the reported information. If there is no request from the eNB 205, the UE retains the logged information.
The UE 200 transitions to the idle mode at step 245 and, if the measurement duration has not expired, continues MDT operation to collect MDT measurement information at steps 250 and 255. The measurement duration may be configured in consideration of the time of the connected mode or not. If the measurement duration expires at step 260, the UE stops MDT. Afterward, the UE 200 enters the connected mode at step 265 and performs MDT measurement report procedure at step 270. That is, the UE 200 notifies the eNB 205 of the presence/absence of the logged MDT measurement information and, if the eNB 205 requests, reports the logged the MDT measurement information.
If the MDT procedure is performed in the situation where a plurality of PLMNs exists, there is a need of a method for controlling the MDT efficiently.